Although in many ways it has similarities to Aphelodoris gigas, which was recently described from Western Australia, your animal the suctorial sponge-feeding dendrodorid, Dendrodoris fumata. It is very similar to forms of D. nigra, but in that species there are 10 -15 small gills forming a cup-shaped circle around the anal papilla, while in D. fumata there are a few [5? 6?] large gills which expand out to cover the posterior half of the body. The thin yellow 'cylinder' you can see at the front of the gills is the faecal string which has been expelled from the anus. From its colour we can be prety sure it has been eating a yellow sponge - probably the one we can see the left side of the top photo.